Nowadays, pre-filled syringes in which a chemical liquid is filled in advance are increasingly used because of their greater convenience of use and prevention of misuse. The rubber members of such a pre-filled syringe are directly in contact with a chemical liquid until the syringe is used. Therefore, often used are butyl rubber-based gaskets and nozzle caps which have excellent chemical resistance, gas permeation resistance, water vapor permeation resistance, and aging resistance.
When a butyl rubber member is used as a gasket or a nozzle cap, the inner wall surface of the syringe and the rubber surface of the gasket or nozzle cap are coated with an oil-type or curable silicone as a lubricant in order to improve sliding properties of the gasket or prevent firm fixing of the nozzle cap. However, the quality of some kinds of preparations may be seriously adversely affected by the silicone coating agent fallen off the barrel inner wall or rubber member as a foreign substance. Also, some bio-preparations are susceptible to interaction with substances eluted from the rubber materials. In order to solve these problems, silicone-free glass or resin pre-filled syringes have been developed by laminating a fluororesin film or the like onto a rubber.
However, the use of a polytetrafluoroethylene (PTFE) film which has a low friction coefficient does not always provide sufficient sliding properties. A known method for achieving both sealing performance and low sliding resistance is to set the compression ratio and contact area within specific ranges (Patent Literature 1). However, the method is not always sufficiently effective. Another known method is a method in which a plurality of annular ridges are formed continuously and integrally at a front portion of a gasket to satisfy both sealing performance and low sliding resistance (Patent Literature 2). However, the method has difficulty in forming thin annular ridges on a mold.